Bobcat 743 Spool issue

[264Chief]

Anyone had this issue...?

I bought a beat up old Bobcat 743 and it mostly worked as it should. The tilt spool forward seal had a good leak and the boom down pressure seemed off almost like the cylinders were binding up when going down and the float function didn't really work.

I decided to replace all the seals, detent balls, springs, plug & o-ring and boots. The spools were a pain to get in and out (as they had a tight fit that made it difficult).

I put it all back together now my boom only goes up regardless of what direction I push the pedal. There doesn't seem to be any tilt function either. Float works (that's how I lower the boom while I'm trying different fixes.

All of my research points to the aux being stuck on but that doesn't seem to be the culprit. I've taken the aux spool out and made sure everything looked good and it seems to go in and out of the detent freely.

It's one of the 4 valve control units
1990 743 with the Kubota

 

[HarleyHappy]

Sounds like a spool is binding up. They can be a pain. What O-rings did you use and did you put any oil or grease on them, putting them in?

 

[264Chief]

Sounds like a spool is binding up. They can be a pain. What O-rings did you use and did you put any oil or grease on them, putting them in?

I used the orange seals. No o-rings on these spools. I don't think they are binding up. They all move freely it just seems like the pressure is bypassing. Only boom up pressure (both pedal directions) and it looks like I have pressure slowly pushing the tilt down (not commanded).

 

[264Chief]

Sounds like a spool is binding up. They can be a pain. What O-rings did you use and did you put any oil or grease on them, putting them in?

And I did not grease or oil them. I did spools while they were still in the bobcat and figured there was enough hydraulic oil.

 

[Align Machine Company]

Spools should not be tight in their respective bores, they are essentially slip fit with only oil film making up the clearance. Did the spools have any wear or marks on them? Did you ensure no internal leakage between valve sections? Lift spool could be receiving all or most flow resulting in its function only.

 

[264Chief]

I didn't notice any damage on the spools when I inspected them.

How would you go about checking for internal leakage?

 

[Align Machine Company]

Are you familiar with micro leak testing?

 

[264Chief]

I am not but... I can look into it.

Would any of the check valves allow this kind of bypassing if one got debris stuck in it or something?...

There is a good possibility I will end up removing the whole assembly I the next week or two to really inspect it.

 

[Align Machine Company]

if the valve has load check poppets, they could possibly be hung up by debris... I would ensure all spools are centered, then disconnect the lift/lower output function lines (leaving valve and going to cylinder) and connect a enerpac pump with a gauge and slowly pressurize the spool, this should hold roughly half system pressure for awhile. You need to test both lift/lower. Then do tilt circuit, if theres internal leakage you will either not build pressure, lose pressure quickly, or another function will operate from your test function. this test is done without removing the valve and machine not running

 

[264Chief]

Okay, next time I tinker on it I'll check and see if it has poppets. I'm taking a day or two off from getting my butt kicked by it lol

I'll see if I can borrow one of those enerpac units. And do some testing.

Thank you guys for your time and info!

 

[264Chief]

Well guys I'm an idiot! I noticed today that my rear aux spool wasn't quite centered and now everything works as it should.

I'm sure my front aux was probably stuck on at the beginning but after putting everything back together I must have slacked on looking at the rear aux spool.

Next up Bobtach bushings and many leaks to chase!

Thanks again for everything guys!